Step by step
- Confirm the drain is gravity. Check the system: sanitary, vent and storm drainage run by gravity and keep their slope; pumped drainage is a pressurised pipe.
- Move the other service. Treat the drain as fixed and offset or reroute the other element over, under or beside it, with the usual clearances and the fewest fittings.
- Watch the other service's own limits. A condensate line also needs its fall, so it may move sideways but not up or down; a pressurised pipe that dips under a drain needs a drain valve at the new low point.
- Escalate what cannot move. If the drain clashes with structure or another fixed element, record the clash with its reason for the plumbing engineer: re-grading the drain changes its fall from end to end.
- Re-test. Re-run the clash test on the drain and the moved service, including the stretch beyond the change.
How ClashFree handles it
Gravity drainage (sanitary, vent, storm) is hands off in ClashFree's base rules: it is never moved, by the AI or by any option. When a drain clashes with a service ClashFree may move, that service gives way; when the drain would have to move, the clash is flagged for a person or sits in the Coordination list.
Lines with a fall, such as condensate, never move up or down: ClashFree refuses vertical offsets for them and keeps reroutes level. A vertical gravity stack is flagged too, since stack offsets carry code limits ClashFree does not check.
A project can add its own hands-off classes in its coordination profile, for example sprinkler mains where the fire engineer must approve every change.
Every fix is a preview inside one Revit transaction group: ClashFree applies it, checks that the clash is gone and that no new clash appeared against the host model and the linked models, and shows you the result. Keep commits it as one undo step; Reject restores the model exactly. Linked models and other trades' elements are never edited.
help/img/gravity-drain-flag.png