1. Understanding Cockroaches that infest the bathroom.
American cockroaches are the larger in size and usually red, which usually breed or search for warm and moistured environment in order to live and multiply. So american cockroaches in particular are those that infest bathrooms and can be eliminated using poisons and traps. But before we go into killing them directly, the best way to get rid of roaches and never have them come into your house again is to make the environment unfavourable for their infestations.
Dehumidifier is the most appropriate device that makes the bathroom very unfavourable to roaches. It works fine in making the room less humid therefore setting them off out of the apartment. There's no harm in having the minimum relative humidity in the bathroom forasmuch as it is for a short time, and when the cockroaches are no more you might stop using it.
Sealing Cracks and Crevices.
Cockroaches do not appear in the bathroom just like the way a toilet can magnet roaches through underground water sources. Check out holes, cracks and many other spaces around the bathroom and seal them to make sure that pest do not infest so easily. This would help to deter the present population of roaches in bathroom and also have clear chance and ideas how to get rid of roaches without any fear of having them anymore.
Dusting with Chemical substances.
This should be done in the evening when roaches usually come out due to love of darkness and warmth. Chemicals that are very suitable in getting rid of cockroaches in bathroom is boric acid and many more alike. If the substance is irritative to your breath it is very wise to use just the toilet disinfectant. Sprinke it all over the places that roaches are obvious to traffic and you should find their corpses the next day. Another alternative is the common ant killer powder, which worked very fast in killing cockroaches in bathrooms. Just dust the places the area with the powder excessively and every hole that roaches obviously hide. In some cases, you might mix the powder with small amount of water to make something like a thick tea and sprinke it all around the sink and corners.
Using Ice and Oil.
Have you every observed that cockroaches are fund of hidding inside the sink? Apart from the sink, cockroaches like holes to make them feel warmer, since their skin needs more moisture. Simply get a "waste oil" of any type about a litre and pour it down the sink at once. Get some blocks of ice and pour it also to fill like half of the sink and leave the to dissolve easily. Oil makes them instantly unproductive and the ice can kill some, especially the younger once that are more used to warmth. At once you've caused a real unfavourable environment that all the cockroaches would get away. Repeat the process atleast 3 times a week in order to make sure there's no life inside that sink.
Getting rid of roaches that solely depend on warmth.
While using ice on cockroaches that are deep inside the pipe worked well, still there must be other little ones outside that you need not to see them quickly. In the sense that they solely depend on warmth and moisture (the red and bigger cockroaches) of the bathroom, making the bath room more cooler might help. Make sure you allow the bathroom opened all night to let breeze accumulate and use the other ideas to kill the rest.
Eliminating Roaches using light.
Light should stay on all day and night so there would be no chance for them to come out. Darkness favour the breeding of roaches everywhere and if you try to keep the room with more light. They would stay in and die without even seeing them anymore. If lighting doesn't seem to hinder them from coming out then definitely, cooling would kill them more easily.
Using Sticky Traps.
Sticky traps can be used on walls were roaches traffic more, floor and corner of the bathroom in order to catch them. It is very effective in the sense that no cockroach that passes along or near the trap cannot be cough and so, you are going to catch many before the end of the day.
Poisoning everything in the bathroom.
Research and observation clears that most cockroaches in the bathroom drink from the water drops or left overs of liquid from the bath and other places, floor or sink. So contaminating everything is more than just to see them and kill manually. Use disinfectant of any type or chemicals that work for ants and mix with water. Pour them all over, flushing the clean one to be replaced by the poisoned liquid.