A pressure-dosed system uses a pump or siphon to deliver effluent to the drainfield in timed doses through a network of small pressurized pipes, instead of letting it flow continuously by gravity. Dosing spreads effluent more evenly across the entire field and lets the soil rest between doses, which can make a field perform better, or make a smaller field work, compared with gravity flow on the same soil.
Where a gravity system tends to load the trenches closest to the tank more heavily than the far end, pressure distribution pushes effluent through the whole network at once via a manifold of small holes, giving much more even loading across the field’s full footprint. That more even loading is part of why pressure dosing is often required, not just optional, on fields with lower application rates or where using field area efficiently matters most.
The tradeoff is mechanical complexity: a pressure-dosed system needs a pump chamber, a pump, floats or timers to control dosing, and electricity, all of which are additional components that a gravity system does not have and that need periodic checking.
Pressure dosing is also used where the drainfield sits above or at a distance from the tank such that gravity alone could not reach it, which is common with mound systems and some sites with unusual topography.
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Timed dosing spreads effluent more evenly across the whole drainfield and lets the soil rest between doses, which can improve field performance or allow a smaller field on the same soil compared with continuous gravity flow.
The pump chamber, pump, and float or timer controls need periodic checking, since they are mechanical and electrical components a gravity system doesn't have.
Guide last reviewed 2026-08-31.