Whilst I am a seed collector, Sandra, I have never collected tomato seeds. Firstly, do you just grow one variety of tomato? If you have two or more in the same greenhouse or close to each other they will cross-pollinate and the plants from the seed you collect will not be the same as the parent.
Tomatoes are a fleshy fruit and so you will need to separate the seed from the flesh. I use a nylon 'flour' sieve for this and wash them in a sink of cold water to get the seed as clean as possible. Dry the seed out in a warm, airy place (NOT the oven) aned then store in a paper packet in the fridge until next year. Good luck.

One thing tomato seed collectors do is put the seedy pulp from the tomato pockets of the fruit, and let it ferment in airtight containers. This breaks down the gel around the seeds and makes them easier to wash.

i just lay mine on kitchen towel on the window sill until dry. then wrap them in clean paper and store in an airtight tub in the cold coalhouse. Dont always get the same tom as previously but they all eat well.

thank you for your answers....cross polination might be interesting as i have grown ten old fashioned varieties....

ooh I bet they taste wonderful. which ones have you grown. I grew Banana cream, Lemon tree [both yellow], christmas grape and another that i cant remember. they were all really tasty too.

i love the yellow ones too Sbg. i have ildi (small yellow grapelike) amish gold soooo sweet, thenn there japanese trifle black..the best with cheese, german red strawberry huge fruit but great for slicing in sandwich es, jersey devil ...look like pepper but taste lovely.....i just love all the shapes and sizes.

must try others. this year i have shirley and ailsa craig as well as collected seed from sun gold and roma.