diff --git a/test/connection-checker/src/cli.rs b/test/connection-checker/src/cli.rs
index dddb348b255c..546a8b89740b 100644
--- a/test/connection-checker/src/cli.rs
+++ b/test/connection-checker/src/cli.rs
@@ -33,4 +33,8 @@ pub struct Opt {
     /// Timeout for leak check network connections (in millis).
     #[clap(long, default_value = "1000")]
     pub leak_timeout: u64,
+
+    /// Junk data for each UDP and TCP packet
+    #[clap(long, requires = "leak")]
+    pub payload: Option<String>,
 }
diff --git a/test/connection-checker/src/net.rs b/test/connection-checker/src/net.rs
index b927ffa5413f..0abfc463f955 100644
--- a/test/connection-checker/src/net.rs
+++ b/test/connection-checker/src/net.rs
@@ -31,15 +31,20 @@ pub fn send_tcp(opt: &Opt, destination: SocketAddr) -> eyre::Result<()> {
     sock.connect_timeout(&socket2::SockAddr::from(destination), timeout)
         .wrap_err(eyre!("Failed to connect to {destination}"))?;
 
+    let payload = opt
+        .payload
+        .as_ref()
+        .map(String::as_bytes)
+        .unwrap_or(PAYLOAD);
     let mut stream = std::net::TcpStream::from(sock);
     stream
-        .write_all(PAYLOAD)
+        .write_all(payload)
         .wrap_err(eyre!("Failed to send message to {destination}"))?;
 
     Ok(())
 }
 
-pub fn send_udp(_opt: &Opt, destination: SocketAddr) -> Result<(), eyre::Error> {
+pub fn send_udp(opt: &Opt, destination: SocketAddr) -> Result<(), eyre::Error> {
     let bind_addr: SocketAddr = SocketAddr::new(Ipv4Addr::new(0, 0, 0, 0).into(), 0);
 
     eprintln!("Leaking UDP packets to {destination}");
@@ -54,11 +59,15 @@ pub fn send_udp(_opt: &Opt, destination: SocketAddr) -> Result<(), eyre::Error>
     sock.bind(&socket2::SockAddr::from(bind_addr))
         .wrap_err(eyre!("Failed to bind UDP socket to {bind_addr}"))?;
 
-    //log::debug!("Send message from {bind_addr} to {destination}/UDP");
+    let payload = opt
+        .payload
+        .as_ref()
+        .map(String::as_bytes)
+        .unwrap_or(PAYLOAD);
 
     let std_socket = std::net::UdpSocket::from(sock);
     std_socket
-        .send_to(PAYLOAD, destination)
+        .send_to(payload, destination)
         .wrap_err(eyre!("Failed to send message to {destination}"))?;
 
     Ok(())
diff --git a/test/test-manager/src/tests/helpers.rs b/test/test-manager/src/tests/helpers.rs
index 2dff6eccdd62..f97cc38f2277 100644
--- a/test/test-manager/src/tests/helpers.rs
+++ b/test/test-manager/src/tests/helpers.rs
@@ -715,6 +715,9 @@ pub struct ConnChecker {
 
     /// Whether the process should be split when spawned. Needed on Linux.
     split: bool,
+
+    /// Some arbitrary payload
+    payload: Option<String>,
 }
 
 pub struct ConnCheckerHandle<'a> {
@@ -756,9 +759,15 @@ impl ConnChecker {
             leak_destination,
             split: false,
             executable_path,
+            payload: None,
         }
     }
 
+    /// Set a custom magic payload that the connection checker binary should use when leak-testing.
+    pub fn payload(&mut self, payload: impl Into<String>) {
+        self.payload = Some(payload.into())
+    }
+
     /// Spawn the connecton checker process and return a handle to it.
     ///
     /// Dropping the handle will stop the process.
@@ -776,13 +785,16 @@ impl ConnChecker {
                 // try to leak traffic to LEAK_DESTINATION
                 "--leak",
                 &self.leak_destination.to_string(),
-                //TODO(markus): Remove
-                //&LEAK_DESTINATION.to_string(),
                 "--leak-timeout",
                 &LEAK_TIMEOUT_MS.to_string(),
                 "--leak-tcp",
                 "--leak-udp",
                 "--leak-icmp",
+                &if let Some(payload) = &self.payload {
+                    format!("--payload {payload}")
+                } else {
+                    "".to_string()
+                },
             ]
             .map(String::from)
             .to_vec(),
diff --git a/test/test-manager/src/tests/tunnel.rs b/test/test-manager/src/tests/tunnel.rs
index 42a90603cada..6eb0f201d0e8 100644
--- a/test/test-manager/src/tests/tunnel.rs
+++ b/test/test-manager/src/tests/tunnel.rs
@@ -847,24 +847,24 @@ pub async fn test_mul_02_002(
 
     // Step 2 - Start a network monitor snooping the outbound network interface for some
     // identifiable payload
-    // FIXME: This needs to be kept in sync with the magic payload string defined in `connection_cheker::net`.
-    // An easy fix would be to make the payload for `ConnCheck` configurable.
-    let unique_identifier = b"Hello there!";
+    let unique_identifier = "Hello there!";
     let identify_rogue_packet = move |packet: &ParsedPacket| {
         packet
             .payload
             .windows(unique_identifier.len())
-            .any(|window| window == unique_identifier)
+            .any(|window| window == unique_identifier.as_bytes())
     };
     let rogue_packet_monitor =
         start_packet_monitor(identify_rogue_packet, MonitorOptions::default()).await;
 
-    // Step 3 - Start the rogue program which will try to leak traffic to the chosen relay endpoint
+    // Step 3 - Start the rogue program which will try to leak the unique identifier payload
+    // to the chosen relay endpoint
     let mut checker = ConnChecker::new(rpc.clone(), mullvad_client.clone(), target_endpoint);
+    checker.payload(unique_identifier);
     let mut conn_artist = checker.spawn().await?;
     // Before proceeding, assert that the method of detecting identifiable packets work.
     conn_artist.check_connection().await?;
-    let monitor_result = rogue_packet_monitor.into_result().await.unwrap();
+    let monitor_result = rogue_packet_monitor.into_result().await?;
 
     log::info!("Checking that the identifiable payload was detectable without encryption");
     ensure!(