A blocked bath or shower leaves standing water around your feet. Hair mixed with soap scum is the usual cause. It forms a dense plug in the trap or the waste pipe.
Shower trays often have small traps, so they clog fast. A hair catcher over the plughole stops most hair before it enters the pipe. Clean it after each use, because a full catcher stops working.
If the bath is still slow after you clear the plughole, look at the other fixtures. When the basin or toilet is slow too, the blockage may sit in the shared waste pipe. Then an engineer will need rods, a snake or a small jetter, since a hair catcher cannot help.
The engineer lifts the plughole cover or waste fitting to reach the trap. Hair and debris near the top often come out first, while deeper plugs need a tool.
A flexible snake goes along the waste pipe to break up the plug. A cutting head helps with compacted hair and soap, because plain rods can bounce off it.
Water runs through the cleared pipe to wash out what is left. A small jetting nozzle can clean the pipe wall when the build-up is heavy, since rods only open a channel.
Fill the bath or run the shower to check the flow. If it still gurgles or drains slowly, ask the engineer what else could be causing it, because a partial blockage may remain.
Prices vary because access and the position of the blockage differ. A shower tray with tight access can take longer than an open bath trap.
Ask for a written quote before work starts, so you can compare it. Ask whether there is a call-out charge, and ask what the quote covers if the blockage is further along the pipe than expected.
Fit a hair catcher over the plughole, since it stops most hair entering the pipe. Clean it after each use. Run water through the plughole now and then, because a trap that dries out can smell.
Most slow baths have a partial blockage in the trap or pipe. Less often, the pipe has a poor fall, or air cannot get in behind the water. An engineer can check for each cause, so describe the symptoms when you ask.
It can, if the bath shares a waste pipe with other fixtures. A blockage in the shared section can slow the bath, the basin and sometimes the toilet. If several fixtures are slow, the blockage is probably in the main waste pipe, since one trap cannot cause that.