terry, I've a bloody 6x2x2 housing an aro.
The door of most hdb allows either width or height <2.5ft. Yours is 4x2x2.5 so it's ok but if it's 4x2.5x2.5 I'm not so sure. One part - either width or height should be <2.5ft.
I have a friend who kena this 5x2.5x2.5 and cannot get into his house. Last resort, tank maker has to cut the silicon and assemble in house. More costly