Backwashing Applies to Sand and DE Filters Only
Before starting: backwashing is the cleaning method for sand and diatomaceous earth (DE) filters. Cartridge filters — which are the most common filter type in Las Vegas residential pools — are not backwashed. They're cleaned by removing the cartridge element and rinsing it with a garden hose. If you have a cartridge filter, see our cartridge filter cleaning guide →
Sand filter: has a multiport valve and a sand bed inside the tank. Usually has a sight glass — a small clear window on the waste line where you can watch the water clarity during backwashing.
DE filter: looks similar to a sand filter with a multiport valve, but the tank contains internal grids coated with diatomaceous earth powder rather than a sand bed.
Cartridge filter: a sealed tank with no multiport valve — just a lid that unscrews or a band clamp that holds the top on. Inside is a cylindrical pleated cartridge. Never attempt to backwash a cartridge filter; the design doesn't support it and you'll damage the cartridge. See our cartridge cleaning guide →
When Should You Backwash?
The most common mistake pool owners make with backwashing is doing it on a calendar schedule rather than reading the actual indicator. Backwashing too frequently wastes water and can disrupt a properly loaded DE filter. Not backwashing when needed restricts flow through the entire system, stresses the pump, and reduces filtration efficiency. The right trigger is always the pressure gauge.
The 8–10 PSI Rule — Your Real Backwash Signal
Document your filter's clean operating pressure immediately after a backwash and rinse cycle. When the gauge reads 8–10 PSI above that documented baseline, it's time to backwash — regardless of when you last did it. Never let pressure rise beyond 15 PSI above baseline before acting; that level of restriction puts strain on the pump and plumbing.
| Situation | When to Backwash |
|---|---|
| Normal operation | When pressure reads 8–10 PSI above clean baseline — typically every 4–6 weeks |
| After a major wind or dust storm | Check pressure within 24–48 hours — desert dust can load a filter overnight |
| After treating a green pool | Backwash when pressure rises 8 PSI; may need multiple cycles over 24–48 hours |
| After heavy bather use | Check pressure the day after — oils, sunscreen, and organics load filters fast |
| After adding DE powder | Backwash when pressure rises — never add DE to an already-clogged filter |
Understanding the Multiport Valve
The multiport valve is what makes backwashing possible. It's a large rotary valve — typically mounted on top of or beside the filter tank — that routes water through different flow paths inside the plumbing. By rotating the handle to different positions, you can direct water to filter normally, flow backwards through the media for backwashing, rinse the media, or bypass the filter entirely.
Most residential multiport valves have six positions. Understanding what each one does is important — using the wrong position at the wrong time can send unfiltered water back to the pool, discharge water you wanted to keep, or bypass chemistry you just added.
Multiport Valve Positions — What Each One Does
Always turn the pump off completely before rotating the valve. Never move the valve handle while the pump is running.
Step-by-Step: How to Backwash a Pool Filter
The full backwash process takes 10–15 minutes and follows the same sequence every time. Work through these steps in order — skipping the rinse step is one of the most common mistakes, and it sends loosened debris back into the pool water instead of out through the waste line.
Turn Off the Pump
Turn the pump off completely — at the timer, controller, or breaker — before touching the multiport valve. This is not optional. Rotating the valve under pressure damages the internal spider gasket, the rubber component that seals each port and routes water correctly. A damaged spider gasket causes simultaneous flow to multiple ports, creating leaks and bypassing filtration — an expensive repair that's completely avoidable by waiting until the pump stops.
Note Your Current Pressure Reading
Before moving the valve, make a mental note of the elevated pressure that triggered the backwash. After the backwash and rinse are complete, you'll compare the new reading to your clean baseline to confirm the cleaning was successful. If pressure doesn't drop close to baseline after a full backwash cycle, the media may need more attention — DE filters may need grid cleaning, sand filters may need sand replacement if the media has channeled.
Connect the Waste Line — Confirm Discharge Route
Before starting the backwash, confirm your waste line is connected to a proper discharge point. In Las Vegas Valley, backwash water must discharge to the sanitary sewer through a clean-out connection — not to the street, yard, landscape, or alley. If your equipment pad isn't already plumbed to a sewer clean-out, backwash water needs to be routed there before beginning. See the full Las Vegas discharge rules section below.
Set the Valve to Backwash
With the pump off, rotate the multiport valve handle to the Backwash position. On most valves, this is labeled clearly on the valve body — usually positioned roughly opposite the Filter setting. If your valve has a locking ring or push-to-turn mechanism, depress it before rotating and confirm it seats into the detent position rather than sitting between two settings.
Turn the Pump On and Run for 2–5 Minutes
Turn the pump back on. Water will now flow backwards through the filter media — entering from the bottom, forcing debris up through the sand or DE powder, and exiting through the waste port and out the waste line. You'll see dirty, discolored water exiting through the waste line or sight glass at first — brown, grey, or cloudy depending on what's been accumulating in the media.
Run the backwash until the water visible through the sight glass runs clear — typically 2–5 minutes. Clear water means most of the accumulated debris has been flushed out. Don't stop too early (debris left in the media will quickly reload) and don't run much longer than needed once the water clears (wastes water without additional benefit).
Turn Off the Pump — Set to Rinse
Turn the pump off, then rotate the valve to the Rinse position. Turn the pump back on and run for 30–60 seconds. The rinse step flows clean water through the filter media in the normal direction, but still routes the outflow to the waste line rather than back to the pool. This re-settles the media (especially important for sand, which has been churned up by the backwash flow) and flushes any remaining loosened debris out through waste rather than returning it to the pool.
Skipping the rinse step is the most common backwash mistake. Without it, loosened debris that didn't make it out during backwash gets sent directly back to the pool when the valve returns to Filter position.
Turn Off the Pump — Set to Filter
Turn the pump off, then rotate the valve back to the Filter position. For sand filters, you're ready to restart. For DE filters, you must add fresh DE powder before restarting — see the DE Recharge section below. Do not run a DE filter without DE powder on the grids; the grids themselves will become the filter medium and will clog rapidly, and uncoated grids are difficult to clean.
Restart the Pump and Check the Pressure Gauge
Turn the pump back on and watch the pressure gauge as it comes up to operating pressure. The reading should be at or close to your documented clean baseline — a significant drop from the elevated pressure that triggered the backwash confirms the cleaning was effective.
If pressure doesn't return close to baseline after a proper backwash and rinse, the media may need deeper attention. Sand filters with compacted or channeled sand may need sand replacement. DE filter grids that are heavily scaled with calcium may need a chemical cleaning. If this has been an issue over multiple backwash cycles, call us at (725) 210-7444 for a filter service.
DE Recharge — Adding New DE Powder After Backwashing
Every time a DE filter is backwashed, the diatomaceous earth powder that coats the internal grids is flushed out along with the debris it captured. The filter's filtration ability comes from that powder — without it, the bare grids filter far less effectively and clog quickly. Recharging with fresh DE powder is a required step after every backwash, not optional.
How to Recharge a DE Filter
Always complete the full backwash and rinse cycle before adding DE powder. Add the powder while the pump is running in Filter mode — it distributes through the system and coats the internal grids evenly as water flows through.
- 1After setting the valve back to Filter, keep the pump off. Determine how much DE powder your filter requires — the amount is specified in your filter manual, typically expressed in pounds. Standard residential DE filters require 1–6 lbs depending on filter size. Never guess — too little under-coats the grids, too much can restrict flow.
- 2Measure the correct amount of DE powder. Wear a dust mask or respirator when handling DE powder — the fine silica particles are harmful if inhaled. Gloves are also recommended.
- 3Mix the DE powder with water in a bucket — typically a slurry of about 2 parts water to 1 part DE by volume. This prevents the dry powder from clumping when it hits the wet skimmer.
- 4Turn the pump on to Filter mode. Allow it to reach operating speed and confirm water is flowing to the pool through the return jets.
- 5Pour the DE slurry slowly into the skimmer basket — the running pump draws the mixture through the system, where it coats the internal filter grids evenly.
- 6Check the pressure gauge. After the DE is fully distributed — typically within 1–2 minutes — the pressure will settle at your clean baseline. If pressure is higher than expected, you may have added too much DE or the grids need cleaning.
Where Backwash Water Must Go in Las Vegas
This is the most commonly misunderstood aspect of backwashing in Las Vegas. Backwash water — like pool drain water — cannot be discharged to the street, alley, landscaping, or yard anywhere in Las Vegas Valley. It must go to the sanitary sewer system through a proper clean-out connection. This rule applies in every jurisdiction in the valley, and violations carry real fines.
Las Vegas Valley Backwash Discharge Rules
Discharging backwash water to the street, yard, or landscape is illegal throughout the Las Vegas Valley under water quality regulations enforced by each municipality. The backwash waste port on your filter must be plumbed to a sanitary sewer clean-out — typically located at or near the equipment pad. If your existing plumbing routes to the street or drains to the yard, it should be corrected.
If you're unsure where your backwash water is discharging, trace the waste line from your multiport valve during a backwash cycle — it's usually a 1.5–2" pipe running from the waste port on the valve. Contact your local water authority with questions:
Filter Pressure Not Recovering After Backwash?
That usually means the media needs a deeper clean or replacement. We diagnose and fix it right the first time.