(thinking out loud)the pumps at the bottom is pumping into a central pipe and jets, is this an external tap of the central pipe to clear the last half cup of water that didnt return to the reservoir to avoid blocking the jets or to hook to another unit: but the pump doesnt look big enough? If you had jets that could control flow and then turned them all the way off wouldnt that flow the water past the jets out the reservoir and provide drainage, there is no other outlet except to use a bucket- i reckon drainage by pump and turning the sparay jets of tight.