Found the answer. There is an easy syslog tester made by Kiwi. Downloads "Kiwi SyslogGen"
I was able to send TCP traps to the Syslog Viewer and they worked. I will contact the vendor to find out why our equipment is not sending messages.
Can you clarify: did you find advanced config from SolarWinds Syslog service?
I would like to get TCP syslog messages also to Syslog service, because I would not like to spend money on additional Syslog service which supports TCP.