The World Bank Enterprise Surveys (my current favourite database) asked companies whether they were requested to make an informal gift when applying for connections for utilities (electrical, water, or telephone connections). The summary results in the Great Lakes region are shown.
(Data shows percentage of companies saying yes)
An informal gift or payment was requested when recently applying for an electrical connection?
An informal gift or payment was requested when recently applying for a water connection?
Burundi No data
An informal gift or payment was requested when recently applying for a telephone connection?
It looks like most corruption was experienced in the DRC, then in Burundi, and the least was experienced in Rwanda.
It doesn't surprise me that Rwanda has such a low level, from personal experience of the place (for what that's worth). However, a major caution on the data is that companies may be particularly unwilling to report honestly on their corruption experience. Reporting an official's dishonesty could result in the official or colleagues punishing the complainant in some way, or could be an admission of crime by the company. Although the surveys are being collected by World Bank contractors, there is the risk that the people handling the data will report back to government or use it for personal advantage. If I was a manager in a company in similar circumstances, I'd say there was no corruption even if there was.