or route it back through the filler cap, so you don't waste the fluid. If you need to drain the tank, then simply remove the pipe from the top of the filler cap, or pull out the pump.

or route it back through the filler cap, so you don't waste the fluid. If you need to drain the tank, then simply remove the pipe from the top of the filler cap, or pull out the pump.

i would route it back into the top of the tank, as without a nozzle on the end to reduce flow and spray the water, you will drain your tank pretty quickly

OR, you could use a typical generic washer line non-return valve, facing the wrong way.