The house smells of sewer after the long trip: it is almost always dry plumbing, not broken plumbing

A house that comes back from a trip smelling wrong has, nine times in ten, a plumbing system that simply dried out while you were gone - and the fix costs a bucket. Every drain in your home is guarded by a bend of trapped water called a P-trap: that little U of pipe under the sink exists to hold a plug of water between your nose and the sewer. Water is its only maintenance. Leave for three weeks and some of those plugs evaporate; the gas arrives through the empty bend like a guest with a key.

The restoration pour, in order

• Every unused fixture, a good slug of water: sinks, baths, bidets, the guest toilet (flush twice), and - the one everyone forgets - the floor drains, the gully traps in the car port and the bathroom corners. A bucket with a cup, one pour per drain until you see the water go and hear the gurgle of air moving: that sound is the trap refilling and the house re-sealing.
• The washing-machine standpipe: the drain hose sits in an open pipe - if it dried and shrank from its socket, the smell is coming straight from there; push the hose back to depth and consider the cheap rubber grommet that seals that joint, sold at every plumbing counter.
• Kitchen sink with a double bowl? Run each side; the shared tail-piece trap under the drainboard holds less water than you think, and it is a dry-out artist.
• Give it a day: trap smells fade within hours once sealed; a smell that persists past tomorrow is the start of the next section, not a refill problem.

When it is the plumbing, not the water

Gurgling from a distant drain when the toilet flushes means the system is pulling air through its own vents - a blocked roof vent (nests, a palm frond, a wasp city) is the usual suspect, and that is a ladder-and-camera call for a professional. A smell strongest at the manhole or the soakaway after water runs points to a blockage or a full tank with nowhere honest to go - the emptying schedule is the maintenance, and a soakaway newly wet and stinking in a dry week is the ground telling you it has stopped absorbing. Outdoor smell after rain with a septic tank means the field or pit is surfacing: that one is the vacuum truck's call today, not next month. And the one red flag on this desk's list: a smell that comes and goes with the wind at one specific wall vent is the building breathing sewer gas into the house - that is the licensed person's investigation, and the trap-pour section above is only the polite way to have ruled out the free answer first.

The habit for the next trip

Ask someone to flush the guest toilet weekly - the house's least-used fixtures are its odour capital - or before you leave, pour a tablespoon of mineral oil down each floor drain: it floats on the trap water and slows evaporation to a crawl, which is the old hotel trick, legal in every manual, and worth remembering when the season's trip runs long. Homes should smell of nothing at all; if they do, the bucket list above is the first, cheapest and most correct place to start.