Is there a smell coming from the shower, laundry or floor drain? In bathrooms or laundries not used very often it is not unusual for the U bend in the floor or shower drain to dry out a bit and therefore smells can come wafting back up from the tank or pipes. Or showers used frequently can end up with a buildup of hair, soap, skin debris and oils which some odour causing bacteria love to eat. Laundry drains can also become smelly. For greywater holding tank smells see here.
Quick Fix #1
Pour about 50 ml of Odour Control Concentrate directly down the shower, laundry or floor drain. Then pour approximately 2 cups of clean cold water into the same drain and leave overnight. This gives our good bugs time to get working for you, they will eat up the slime and not produce any smells, instead they produce just carbon dioxide, water and more good bugs.
Better Fix #2
For floor or shower drains put on a pair of rubber gloves, remove the grate, clear out any accumulated hair etc and flush the drain thoroughly with warm water. You may find it useful to carefully hose the drain out with the garden hose which gives you more pressure, but not too much or you could cause a flood.
For laundry sink drains, place a bucket under the sink, unscrew the U bend and clean out any slime or debris. Then reassemble, undersink_gully_traprun some water into the sink and check for any leaks.
Finish off by spraying down the drain thoroughly with Odour Control Spray and respray weekly if necessary. For drains not used very often it may be necessary to periodically flush the drain with warm water, to maintain the protective water trapped in the U bend. Respray each time with Odour Control Spray.
Give these a good flush out with the garden hose and spray with Odour Control Spray. You may need to do this weekly until the good bacteria get gully-trap-1overflow-gully_trapestablished. Make sure you also spray down the drain or plug hole at the sink etc from which the outside drain receives water.