Starting two nights ago, both toilets in my home fill with water when flushed. I tried a toilet snake and plunger on both (multiple times) and the problem still persists. I was only able to get the toilet snake about 2 to 3 feet into the toilets so maybe I haven't gone far enough. Both toilets showed some debris on the initial use of the snake, but not on subsequent attempts.

The regular toilet also leaks water at the floor level when I use the plunger on it and it looks like it also leaks when I use the plunger on the other (low flow) toilet. Using the plunger on the low flow toilet also caused water to go into the shower through the shower drain. The house was built in the 60's and is on a septic system - not sure if there's an actual tank or just a field. We're on a large property out in the country. The septic system was last serviced over 15 years ago.

The shower drains and sink drains all appear to drain normally. Also, after a few hours of non-water use both toilets will flush normally once (the regular toilet) or twice (the low flow toilet) then go back to filling the toilet with water when flushed another time.

Another factor is the kitchen sink which has had an increasingly bad drip for months.

So my questions are: 1) Is there any way to tell if the problem lies in the septic system or in the house plumbing?

2) Any suggestions for what I should try next?