If you’ve set your multiport valve to FILTER and water is still coming out the backwash line — or if you can hear water bypassing internally even though the handle is in the right position — you have a torn or worn spider gasket. The fix is a 30-minute job and a $15–$50 part. Done correctly, your sand or DE filter goes back to filtering at 100% efficiency instead of letting 20–50% of the water route to waste.
What the spider gasket does
Inside every multiport valve is a star-shaped rubber gasket called the “spider gasket” (because of its shape). It sits between the valve body and a rotating valve key that aligns with different port positions (Filter, Backwash, Rinse, Waste, Recirculate, Closed). When you move the handle, the key rotates over the gasket, sealing off the ports you don’t want and opening the ones you do.
Over years of compression and chemical exposure, the rubber flattens, cracks, or tears at the spokes. Once that happens, water finds paths between ports that should be closed — and your filter routes water to waste even on FILTER mode.
How to know it’s the spider gasket
- Water coming out the backwash port or waste line while set to FILTER.
- Water level in the pool dropping unexpectedly during normal operation.
- Filter pressure lower than baseline (water bypassing the filter media).
- Visible water dripping from a sight glass even after rinse mode.
- You can hear water moving through the multiport when the pump is off.
What you’ll need
- A new spider gasket matched to your multiport valve (Pentair/Sta-Rite, Hayward, Jandy, Astral — each brand uses a different gasket shape)
- A flat screwdriver
- Silicone-based pool lubricant
- A clean rag
- Channel-lock pliers
Step-by-step: replacing the spider gasket
Pump off at the breaker. Open the air-relief valve on top of the filter. Confirm gauge at zero.
Most multiports have 6–8 screws or bolts around the top perimeter. Loosen them in a star pattern. Lift the cover (which includes the handle) straight up. The valve key (a vertical shaft with a star-shaped bottom) usually comes up with the cover.
Look at the underside of the cover. The spider gasket is a star-shaped rubber piece pressed into a groove on the bottom of the valve key. Tears, flat spots, or compressed sections are the failure modes. Often the gasket comes out partially adhered to the gasket groove.
Pry the old spider gasket out of its groove with a flat screwdriver, working around the perimeter. Take your time — if the gasket is brittle, it’ll come out in pieces. Pull every fragment out of the groove.
Wipe the gasket groove clean with a rag. Any debris left in the groove will prevent the new gasket from seating flat — which means it leaks immediately on the first run.
A pea-sized amount of silicone pool lube, rubbed lightly over the gasket surface. Don’t glue the gasket in — some forums recommend silicone adhesive; manufacturers say not to. The gasket seats and seals through compression alone.
Match the spider points to the spokes of the groove. Press evenly with your fingers, working around the perimeter. The new gasket should sit flat in the groove with no high spots.
Lower the cover + key straight down so the gasket lands evenly on the valve seat. Reinstall the perimeter bolts in a star pattern, in two passes (finger-tight, then snug). Don’t overtighten — you can crack the cover.
Restart the pump. With the system running, push the handle down and cycle through Filter, Backwash, Rinse, Waste, and Recirculate, leaving 30 seconds between each. Verify only the expected port is flowing water at each setting.
Common spider gaskets in stock
Pentair Multiport Spider Gasket
$34.80
Shop Now
Pentair Sta-Rite 2″ Multiport Spider Gasket
$51.10
Shop Now
Astral 1.5″ Multiport Spider Gasket
$14.20
Shop NowHow long should the new gasket last?
5–10 years is typical with proper care. The single biggest predictor of gasket life is whether you remember to push down on the handle before rotating it. Rotating against the gasket without compressing the spring tears the rubber. Push down, turn, release. Every time.
Not sure which spider gasket fits your multiport? Send PST Pool Supplies the valve manufacturer (Pentair, Hayward, Jandy, Astral) and a photo of the top cover — we’ll match the right gasket on the first try.