Create 4 Types Of Strings Under Same Method But Only Draw One At A Time

I am having trouble with methods. What I want to do is be able to create 4 types of strings under the same method, but only draw one of them at a time.

i.e

UI.initialise;
UI.addButton ("pipe", this::drain);
public void drain(){
this.pipe ("pipe1");
this.pipe ("pipe2");

[Code] ....

When I press the button "drain" it will print=

pipe1

pipe2

pipe3

pipe4

I am having a lot of difficulty just printing one out after each time I press drain.

"drain"

pipe1

"drain"

pipe2 etc..