The toilet tank number is stamped inside the tank, on the back wall near the water line
Lift the tank lid. The tank number is stamped on the inside back wall of the tank, near the water line.
American Standard: a four-digit number; 2 = one-piece, 4 = two-piece. Kohler: "The toilet tank number is imprinted on the inside back of the tank."
American Standard
American Standard: "You'll notice a four-digit number located on the back of the tank, near the water level mark. This number will be stamped into the china or as a stamp with a barcode. This is the tank model number. If the number starts with a two, it is a one-piece toilet. If the number starts with a four, it is a two-piece toilet." (AS Knowledge Base 1122).
American Standard uses this number to identify parts (AS Knowledge Base 1153). Part lists: American Standard parts hub.
Kohler
Kohler's brochure: "Many toilets have service information on the underside of the tank lid. The toilet tank number is imprinted on the inside back of the tank." (Kohler brochure).
Kohler model numbers start with "K", which "may not be included on certain product labels and when stamped onto the product itself". Letters after the base number show a variation: "RA" means right-hand trip lever. The color code follows: "0" is white (Kohler Assist).
TOTO
On a Drake two-piece (TOTO CST743S parts manual):
- CST = the whole gravity two-piece toilet
- ST = tank
- C = bowl
- 743 = model
- S = G-MAX; the 1.28 gpf version uses E (E-MAX) instead (TOTO CST743E manual)
See TOTO Drake ST743.
Mansfield
Mansfield's 137-160 sheet lists model 137 as the bowl and 160 as the tank and cover (Mansfield 137-160 spec sheet). See Mansfield 160.
Sources
- American Standard Knowledge Base, Where can I find the model number of my toilet?: https://faq.americanstandard-us.com/article/1122 (read 2026-10-27)
- Kohler, Toilets Service Parts brochure (PDF, 2020): https://resources.kohler.com/webassets/kpna/brochures/Toilet_ServiceParts_Brochure_FINAL.pdf (read 2026-10-27)
- American Standard Knowledge Base, What information is needed to identify parts for an American Standard toilet?: https://faq.americanstandard-us.com/article/1153 (read 2026-10-27)
- Kohler Assist, Finding a KOHLER or STERLING product model number or serial number: https://assist.kohler.com/en/other-products/Finding-a-KOHLER-or-STERLING-Product-Model-Number-or-Serial-Number (read 2026-10-27)
- TOTO, Parts Manual CST743S Drake 1.6 gpf (PD-00237 v.10, Dec 2021): https://www.totousa.com/filemanager_uploads/product_assets/PartsManual/PD-00237_CST743S.pdf (read 2026-10-27)
- TOTO, Parts Manual CST743E Drake 1.28 gpf (PD-00130): https://www.totousa.com/filemanager_uploads/product_assets/PartsManual/PD-00130_CST743E.pdf (read 2026-10-27)
- Mansfield Plumbing Products, 137-160 Alto 1.6 spec sheet (PDF, Rev. 12/25, linked from mansfieldplumbing.com): https://assets.edgenet.com/78b982d8-88ae-4e3e-a632-feb3a7ba8df6 (read 2026-10-27)