Make sure you have a good reason for the check. It will only be accepted to counter vandalism or disruption to Wikimedia wikis. Valid reasons include needing a block of the underlying IP or IP range, disruptive sockpuppetry, vote-stacking, and similar disruption where the technical evidence from running a check would prevent or reduce further disruption.
Be specific in your reasons. Ambiguous or insufficient reasons will cause delays. Explain the disruption and why you believe the accounts are related, ideally using diff links or other evidence.
Make sure there are no local checkusers or policies.
Reason(s): Dulovokil146 is a known sock from enwiki of PavelStaykov [stalktoy] – [cross-wiki edits], blocked indefinitely there. We've allowed this particular sock to continue editing on bgwiki in the hope that he'll mend his ways after he promised he'll refrain from using other socks and open proxies (which he had extensively and aggressively abused in the past). Unfortunately, his behaviour has so far been on the verge of the acceptable. After numerous altercations, today a new user, 500ГОДИНИСТИГАТ, suddenly popped up and started making edits virtually identical to those of Dulovokil146 (the specific personal insults in the edit summaries are especially telling). Although the duck test passes, it's not entirely impossible that this is in fact another prank of Mitko12. Therefore, an additional confirmation from the CU tools would help us decide if the user has indeed betrayed the community's trust and if a permanent block, like on enwiki, should be imposed. Many thanks in advance! — Luchesar • T/C 11:45, 20 July 2016 (UTC)
Reason(s): User ΣΕ ΘΕΛΩ, interested in "destroying wikipedia", has clearly created some puppets (either he admited or confirmed by duck test) that have been blocked. User 2021..με τα τσαρούχια! was created and his first edits was one saying that he will be blocked because of his name and the other saying "he is new user". Clearly a puppet, but is it from the previously mentioned user. C messier (talk) 21:36, 26 July 2016 (UTC)
2021..με τα τσαρούχια! is a sock of Κακός και Κάκιστος / Εύχρηστο Σπιρτόκουτο. Ruslik (talk) 12:59, 27 July 2016 (UTC)
Reason(s): Users Probajutor and GulubuntzBudulush have been blocked for sockpuppetry and vandalism. User Ajutorulprobei (with a similar name) registered today and seems to follow the same behavioural pattern. It would be extremely helpful for us to have a technical confirmation of our suspicion via CU. Please add any other relevant information needed in order to solve this case (related accounts, including anonymous IPs with disturbing activity). Thank you. --Pafsanias (talk) 12:26, 29 July 2016 (UTC)