From time to time, Maybe once or twice a month, when our basement toilet is flushed, it overflows into the shower/tub. The water in the toilet slowly empties, and if I flush again, the water will stay in the toilet like a regular clog, but if I plung, it all goes into the tub. What do you think is the problem here? Is the clog behind the tub? If so, should I try and plunge the drain in the tub? Or would a snake down the toilet work better.
Thanks

Your tub and toilet share the same drain and the clog is after both of them. You need to snake the drain, roof vent stack would be the best place to start if it's safe to stand on your roof. Run enough rod to reach the toilet and about 15' more. Don't use chemicals since they could also back up into the tub and make further rodding difficult.

I agree, to an extent, with ballengerb1. You should be able to snake the drain through your toilet or a cleanout trap(if you have one) under the sink. You may want to verify that there is even a vent stack in the pipe. This is usually required by building code, but I have been in a number of handyman specials that don't have a vent stack and that could be causing the clogged toilet (http://mycloggedtoilet.com) to begin with.

Aside from that there is little you can do. You may want to start the toilet on a monthly enzyme treatment in an effort to keep these problems down to a minimum.

Coewtails,
Nice thinking outside the box on the vent. But you had to go and spoil it with that bit about enzymes. So he has a vent problem. Enzymes going to help that? Please explain. Regards, Tom