Overflow Traps
Overflow Traps
Multisiphon overflow
Rainwater overflow trap

The Multisiphon overflow trap is a unique unit from WISY® designed specifically for use in rainwater storage tanks. It is fitted inside the tank and connected to a short stub pipe for joining to standard 100mm drain.

The unit incorporates several important features:

  • A water trap to prevent bad odours from the drainage system
  • A surface skimmer to effectively remove floating debris
  • A backflow prevention device*
  • An optional vermin barrier

The unit is effectively a ‘U’ bend providing a water seal in the same way as a WC pan or waste trap. This acts as a barrier to unpleasant smells from the drain that connects to the overflow, which could otherwise taint the water. It also very effectively removes floating debris from the surface of the water, due to the “skimming” design of the unit at the top.

The most important function, however, is to act as an anti-backflow device to prevent a surcharge from the drains entering back in to the tank and contaminating the stored water.

Component Parts
  1. Multisiphon unit with shaped horizontal inlet for skimming water surface.
  2. Stainless steel clamp for secure fixing to outlet pipe.
  3. Brace tube holds base of unit against tank wall.

The unit connects to standard 100mm pipe. Where the tank requires a 150mm connection, two units are manifolded together, or 3 units for connection to 200mm pipe.

All our RainSava GRP tanks are pre-fitted with these devices.

*All rainwater tanks must be protected by a backflow prevention in order to comply with BS 8515 Rainwater Harvesting Systems Code of Practice