Update: Maria asked a good question about whether or not the rubber seals are reusable .. here's what the Tattler Faq/Testimonial part of their website says:
Q: Are the rubber gaskets reusable, and how long will they last?
A: Yes, the rubber gaskets are reusable and will seal numerous times when used as directed. When cared for properly, many years of use may be expected. Testimonials from our satisfied customers report use of rubber rings for more than 20 years!