I don't know of anything that you can use inside of the tank, this is what i would reccomend under the following situations...
If you only have one or two small portable tanks in which your snakes / other reptiles live in...
1) head over to home depot.
2) purchase some ortho indoor/outdoor insect killer. this comes in a trigger spray bottle or in a one gallon bottle that can be pumped up and sprayed.
3) spray the aunt trail and let them die.
4) move the tank spray under it (as long as it's not on fine furniture.) if the tank is glass i'd take it and clean it out with a heavy water/vinegar mixture, rinse it well and put it back.
If you have them in a more permanant non movable cage i'd just do steps 1-4 above. don't let this chemical in the cage. try and move your reptiles into some other place while you spray this no matter which setup you have, because the vapors can be harmful. once this dries, however, it should be harmless to them along with your cat as long as you do not have it in their cage...the cat can walk over it all s/he wants and it wont phase him/her
-----
The reason mainstream thought is thought of as a stream is because it's so shallow. -Unknown