W/C conundrum

Hi Y'all,

First off let me give a massive thanks to Jan and all those who inhabit this forum...it's fabulously helpful and informative.

Here is my query:

My apartment is relatively newly modernised and has a Roca w/c. In a marginally(!) inconvenienced type of a way the designers of the cistern felt it their duty to make life as difficult as possible to access the inside by way of not having any lid to it. The whole damn cistern is a sealed unit...apart from prising off the flusher buttons it is impossible to get inside. 

Is there a friendly plumber who can give me any advice as it takes forever to fill and presumably needs adjusting....I am near the centre of Puerto de Mazerron and will be over there for a few days fro Tuesday this week.

Many thanks for any input.

Cheers...Jeremy