1) The easiest part to start is by drawing a circle .The arrow points the frontal part of what will be our toilet .You can change the point of view just by rotating the semi-circle the way you like.

2)The perpendicular line of the frontal arrow line will be our guide line to draw the back box of the toilet. Just extend a parallel line as illustrated .

3) Just finish the box as illustrated ,draw parallel and perpendicular lines depending the case.