Thetford 23721

Lip Seal (Post-6/15/00)

Thetford 23721 is the lip seal (post-6/15/00) for the Cassette C2 and Cassette C200S-CS and Cassette C4. The seal that sits around the lip of the flush ball or blade opening. Thetford lists it for Cassette C2, Cassette C200S-CS and Cassette C4. It is item 5 on those parts lists.

Which models this fits

  • Cassette C2

    Verified against Thetford Parts List, Cassette C2 (Rev. D).

  • Cassette C200S-CS

    Verified against Thetford Parts List, Cassette C200S-CS (Rev. D).

    Item 5 on this parts list.

  • Cassette C4

    Verified against Thetford Parts List, Cassette C4 (Rev. D).

How to tell which one you have

Find item 5 on your model’s parts diagram — that callout is this part. Check the model on the data plate reads Cassette C2, Cassette C200S-CS or Cassette C4.

Is this part still current?

Yes. Thetford still lists 23721 on its current parts list.

Also worth having before you start

  • Disposable nitrile gloves

    Thetford’s own kit instructions say to wear protective gloves and eyewear when you touch material that has been in contact with human waste, and to disinfect your tools and work surface afterwards. If you do not already have a box in the camper, get one before you start.

  • Thetford seal lube and conditioner

    A new seal lasts longer if it is kept conditioned. Thetford makes this for its own toilets, so it is the maintenance product matched to the part you are fitting.

These are supplies, not replacement parts. We have not matched them to your model, because they do not need to fit anything.

Check this before you order

  • Confirm your toilet is a Cassette C2, Cassette C200S-CS or a Cassette C4.
  • Ignore listing titles that claim one part covers several models unless the manufacturer's parts lists agree.

Current marketplace inventory

Listings from eBay

We verified the part above from manufacturer documents. The listings below are current eBay inventory, and eBay sellers set their own titles, prices and shipping.

Checking current eBay inventory…

Camper Replacement Parts is not the seller. Price, shipping, stock and item condition are set by the eBay seller and can change at any time. We may earn a commission if you buy through these links.

Where our information comes from

We work from the manufacturer’s own documents. We have not installed this part and we do not test parts in a shop.

Last checked 2026-08-29.