u could always just top off ur res and not dump anything i've got 1 res i do that to as it's hard to change and i don't see no diffrence at all i just let it get real low and then just top it off every 2 to 3 weeks and i have'nt had a problem with anything and other than u being stealthy the bag is a good idea if u get the bags i use to work with u buy them at home depot in a big yellow box it's real heavy duty for construction sites thick this would be good if nothing else but to block out light as i have 1 5 gal bucket i do this with not for what ur trying to do but to keep light out as it's not like a reg heafty bag but alot thicker