I have a pair of brick cisterns & they seem to be leaking. I can fill them to the top but they bleed back down & lose about a foot of water level. This leads me to the obvious conclusion that there are some bad masonry joints at that level. Question is, is there any type of spray-on sealant which I could get in there & apply after draining the cistern or should I just resign myself to the fact that I need to get down in there & do it the hard way & pack some hydro seal mortar into the joints? Anyone ever deal with a similar situation? Thanks.