It is not suggested for the main reason unlike a 2" washing machine drain it has no stand pipe before the pee trap. Or a toilet 3" inch drain, it will sometimes flush but leave a little behind that is diluted, with a lid on it to keep the smell down. If you hock it over the bathtub side 1 1/2" drain, the smell will get bad and that is why they suggest the toilet or the washing machine drain. Both hide a smell better. Also think, if you have it hocked over a bathtub and your taking a shower or bath and the CG starts cleaning yes it will drain but do you really want to step in it or have it in your bath water if your soaking?

Now if there is a drain for a tub, but that tub is not in place yet, even if you lift the hose a foot above the CG then to the tub drain the tub drain will not be able to take that much water with out over flowing the drain because the drain is just to small and short unless your able to shove that flexible drain hose down the
pee trap then it might not back flow on you. But don't look at me or CG to guarantee it. CG wants a 2" or larger drain to handle the CG draining.