Sprayer Tank Cleanout & Rinse Clean, Crop Safe

Herbicide residue left in a tank, hoses, filters and nozzles can carry over into the next load and damage a sensitive crop — even a few grams of the wrong product can stunt or kill. Cleaning out between jobs, and especially when switching from a hormone or sulfonylurea herbicide to a sensitive crop, protects yield and avoids costly spray drift-style injury from your own equipment.

A triple rinse empties the tank, then partly refills, agitates and drains it three times. Each rinse dilutes the leftover residue by the same ratio, so the residue that survives is the dilution per rinse cubed. Three modest rinses leave only a tiny fraction — far less than one big rinse using the same total water — which is why the staged method is the standard.

Rinse water per rinse = tank size × rinse ratio (often 10–20% of tank volume). Total rinse water = rinse water per rinse × number of rinses. Residual % = (heel fraction after draining) raised to the power of the number of rinses, expressed as a percentage of the original concentration. The calculator does all three from your tank size and ratio.

It is the share of the original chemical concentration still in the tank after the full cleanout. Because each rinse dilutes by the same factor, the residual falls geometrically: three 10% heels leave roughly 0.1% of the start concentration. The lower this number, the safer the tank is for the next sensitive crop.

A practical rinse uses about 10–20% of the tank's volume — enough to wet all internal surfaces and agitate well. More water per rinse lowers the heel and the residual, but three properly agitated moderate rinses beat one large flush. Always run the rinsate through the boom and nozzles, not just the tank.

Water alone removes most residue, but oily formulations and acidic herbicides often need a cleaning agent — ammonia, a commercial tank cleaner, or for sulfonylureas a chlorine bleach solution — added to one of the rinses and left to soak. Always follow the product label's decontamination instructions; the calculator handles the water volumes, not the chemistry.

Spray the diluted rinsate onto the original target crop or a labelled site at a rate within label limits — that is the recommended route. Never tip it down a drain, into a watercourse, or onto bare ground where it can leach. The total rinse water figure helps you plan a disposal area large enough to apply it legally.

Enter the tank size in whatever unit you work in — litres or gallons — and the rinse ratio as a fraction of that volume; the results come back in the same unit. The residual percentage is unit-free because it depends only on the dilution ratio and the number of rinses, not the absolute tank size.

They are solid planning figures. The real heel left after draining varies with tank shape, sump design, how well you agitate, and the formulation. Treat the residual % as a guide to whether a triple rinse is enough, and add a dedicated tank cleaner or an extra rinse whenever you switch to a high-value sensitive crop.