Code Stories · why the rule exists
Cleanouts: Spacing and Changes of Direction
The rule in Massachusetts today
Verbatim, 10.08(3)(d): "Accessible cleanouts shall be installed: 1. at each change of direction of the building drain; or 2. at each change of direction of horizontal waste or soil lines and branch lines, that are greater than 45 degrees." 10.08(3)(j): "Cleanouts shall be of the same nominal size as the pipes up to four inches and not less than four inches for larger piping." 10.08(3)(k)1: "Cleanouts on three inch or larger pipes shall be so installed that there is a clearance of not less than 18 inches"; 2: smaller than three inches, "a 12-inch clearance."
- Cleanouts every 50 ft on horizontal drains 4 in. and smaller (248 CMR 10.08(3)(a))
- Cleanouts every 100 ft on horizontal drains larger than 4 in. (248 CMR 10.08(3)(a))
Why it exists
Every drain eventually clogs, and a cleanout is the planned way to reach the clog without cutting pipe. Blockages tend to form where the flow slows or changes direction. A cable or snake can only go so far and loses force at each bend, so both distance and bends are limited between access points. Making the cleanout the same size as the pipe, up to a point, lets a full-size tool pass.
How it came to be
- 1940 — BMS 66 section 508 requires cleanouts at the foot of each stack and at direction changes greater than 45 degrees. archive.org
- 1940 — BMS 66 sets a spacing limit. archive.org
- 1940 — BMS 66 counts a bolted fixture connection as a cleanout. archive.org
Make it stick
Mnemonic: 'Every bend is a place to get stuck, so give the snake a door.' MA version: a door at the base of every stack, at every turn of the building drain, at turns over 45 degrees on branches, and at least every 50 ft (4 in. and smaller) or 100 ft (over 4 in.).
On the exam
Expect MA spacing (50 ft for 4 in. and smaller, 100 ft for larger), when a change of direction requires a cleanout (every change on the building drain; more than 45 degrees on horizontal waste, soil and branch lines), the base-of-stack cleanout, cleanout size (same as the pipe up to 4 in., not less than 4 in. above that), clearance (18 in. for 3 in. and larger, 12 in. for smaller), the building-drain cleanout at the foundation wall, the outside cleanout within 5 ft of the foundation wall for slabs and shallow crawl spaces, and MA's cleanout equivalents (10.08(3)(m)): a fixture trap with a union connection, a fixture with an integral trap, or a readily removable roof-drain cover.
What people get wrong
- Cleanouts can be buried or tiled over if you mark where they are. No. MA says cleanout plugs shall not be covered with cement, plaster or any other permanent finish; where one must be concealed, an access plate or door is required (248 CMR 10.08(3)(l)). The 1940 manual likewise required manholes for underground cleanouts that were not flush with the floor.
- Any change of direction needs a cleanout. Partly true in MA. On the building drain, every change of direction needs an accessible cleanout (10.08(3)(d)1). On horizontal waste or soil lines and branch lines, only changes of more than 45 degrees do (10.08(3)(d)2).
Try it: 3 real practice questions
Q1. On waste, soil and branch lines, a cleanout is required at each change of direction greater than:
Sharp turns are where solids settle, so 248 CMR 10.08(3) requires a cleanout at each change of direction greater than 45 degrees on waste, soil and branch lines. The building drain is stricter: it needs a cleanout at every change of direction, whatever the angle.
248 CMR 10.08(3)Q2. On horizontal drainage piping 4 inches in diameter or smaller, cleanouts must be spaced no more than:
248 CMR 10.08(3)(a) limits cleanout spacing to 50 ft on horizontal drain and branch piping 4 in. or smaller, and 100 ft on piping over 4 in. Closer spacing on small pipe keeps every section within reach of a standard drain-cleaning cable. The 75 ft figure applies only to large (over 10 in.) underground runs under 150 ft in 10.08(3)(o).
248 CMR 10.08(3)(a)Q3. A cleanout is required at what location on every drainage stack?
The base of a stack is where vertical flow turns horizontal and slows, so solids pile up there. 248 CMR 10.08(3)(f) requires a cleanout at or near the base of each soil or waste stack so a cable can reach both the stack bend and the building drain. An opening at the top or roof is far from where these blockages usually form.
248 CMR 10.08(3)(f)These come from the PressureTest bank. Start 7 days free for the full bank, timed exam simulations and drawn isometric problems.