I plan to get a plumber to install but would like to choose the replacement toilet bowl (with seat) and cistern. Ideally don't want any exposure of the currently covered parts. Which dimensions would be critical and how do I determine whether the current one is S or P trap. Anything else I need to ensure prior to purchasing a replacement. Note the reason II'm changing this is because there appear s to be a small leak at the base of the current bowl which is causing a constant odour.
